Crude glycerol Crude glycerol is a by-product of the process to obtain biodiesel, namely a transesterification of vegetable raw material, such as natural oils or animal fat, with lower alcohols.
Such a transesterification process is the method most often employed to enable the use of vegetable oils (for instance coconut, soy, castor, sunflower, peanut) and animal fat as fuel, for instance in the presence of a homogeneous or heterogeneous alkaline catalyst.
From the transesterification reaction in a basic or acid medium, one obtains a monoalkyl ester—the biodiesel fuel—and glycerol.
A general equation for that reaction would be: triglyceride+3 alkyl alcohol→glycerol+3 fatty acid alkyl ester
The monoalkyl ester and the glycerol formed in the transesterification reaction are substantially immiscible and are separated by decantation at the end of the reaction.
Very commonly, in that process to obtain biodiesel, the neutralization of the transesterification product with hydrochloric acid gives origin to a sodium chloride contamination solubilized in the decanted glycerin. The presence of sodium chloride accelerates corrosion in stainless steel equipment.
This raw glycerol, byproduct of the transesterification reaction, has low purity and contains, among several contaminants, fatty acids, fatty acid salts, inorganic salts, inorganic acids, inorganic bases, water, lower alcohols, mono-, di- and triglycerides, esters of fatty acids with lower alcohols, transesterification catalyst residue, etc. To enable the use of this raw glycerol, the traditional path has been the removal of its contaminants with several purification steps, to obtain a purer product commonly referred to as blond glycerin, which is then bi-distilled, to reach high purity. It is obviously a long and costly process when compared to the use of the crude glycerol.
Dioxolane and Process to Obtain It
Dioxolanes, in the sense utilized herein, are a group of organic compounds containing the 1,3-dioxolane ring, known to be used in several applications, such as pharmaceutical actives, chemical intermediates and solvents. The particular use as solvent is interesting as it is less harmful than traditional solvents, with similar performance.
The preparation of a dioxolane compound by way of reacting glycerol and a ketone or an aldehyde is generally known, for instance as in the following publications: R. J. Fessenden & J. F. Fessenden, Organic Chemistry, 2nd edition, page 524, 1982 and T. W. Greene, Protective Groups in Organic Chemistry, John Wiley & Sons, 1981. No mention to the use of crude glycerol and the effects of the contaminants upon the reaction is mentioned.